Norton, Viewing And Display Apparatus, U.S. Pat. No. 5,311,203 (May 10, 1994) describes a viewing device for identifying features of interest which appear in the field of view of the device. Though Norton was described in the context of a hand-held star-gazing device, and purported to provide information about asterisms (constellations or groups of stars) in the field of view, the device does not work unless held with certain components held perfectly vertical during use. Any twisting or rotation of the device about the viewing axis necessarily causes errors, and introduces ambiguity that cannot be resolved. Thus, it is not possible to implement the Norton system, as proposed by Norton, in a hand-held device. Norton consists of a box-like housing with a viewing channel therethrough, an LCD display and image overlay system for superimposing an image on the field of view, optics for manipulating the superimposed image to make it appear at infinity, a single axis eccentrically weighted inclinometer to measure inclination of the device and three magnetic sensors to determine the bearing of the device, a database with information regarding the constellations which might be viewed with the device, and a microprocessor. The viewing channel establishes a field of view for the user, through which the user can see constellations. The microprocessor is programmed to interpret sensor input and search the database for constellations in the field of view, and transmit a reference display data to the display.
The Norton system suffers from crippling defects. An operational device depends on perfect vertical alignment of the inclinometer. Without perfect vertical alignment of the inclinometer the device cannot unambiguously determine its orientation. The slightest deviation from vertical introduces ambiguity, such that the device can determine only that the viewing channel is aligned somewhere on a wide arc of the sky. If the device is not held perfectly vertically, that is, if it is twisted or rotated about the viewing axis, projection errors are introduced into the output from the inclinometer, so that the device has inadequate information regarding its inclination. In the case that the twist induced error is small enough that the device can determine its viewing axis with enough precision to generate a reference display that corresponds to constellations in the field of view, the device has no way to determine that it is twisted, and thus cannot rotate the reference display to align with the constellation.
Our own patents, Lemp, Celestial Object Location Device, U.S. Pat. No. 6,366,212 (Apr. 2, 2002) and U.S. Pat. No. 6,570,506 (May 27, 2003) and our pending patent application Lemp, U.S. Publication 20030218546 (Nov. 27, 2003) (the entirety of which is hereby incorporated by reference) provides solutions to this problem. Lemp shows a device for viewing celestial objects from a location at a time and date ascertained by the device, comprising a viewing means to observe along a viewing axis defined by an azimuth angle and a nadir angle or altitude; a processor, a multi-axis magnetic sensor adapted to provide the processor with azimuth data representing the azimuth angle, a multi-axis gravitational sensor adapted to provide the processor with nadir data representing the nadir angle; location means for providing location data representing the location of the viewing device to the processor; time means for providing time and date data representing the time and date to the processor; and a database adapted to be accessed by the processor and provide data such that the processor determines celestial coordinates of right ascension and declination corresponding to the viewing axis based on the azimuth data, the nadir data, the location data, and the time and date data. The device can be used to direct a user to a celestial object (its resolution is very high, so that it can direct the user to individual stars and planets, as well as constellations and asterisms) and it can be used to identify an object to which the user has pointed the device.
The position sensing function of the device is most accurately determined using a three axis magnetic sensor and a three axis gravitational sensor. The use of lesser arrays will generally result in reduced accuracy and resolution of the device, such that it will be desirable to improve the resolution with the methods described below, especially when the devices are embodied in celestial object location devices with magnifying optics.